Contact lens for correcting myopia and/or astigmatism

ABSTRACT

The present invention provides a myopia and/or astigmatism-correcting contact lens for correcting myopia and/or astigmatism based on the alteration in the shape of a patient&#39;s cornea. The myopia and/or astigmatism-correcting contact lens comprises a pressure zone having a first surface defined by the inner surface of the contact lens located on the side of the patient&#39;s cornea and positioned at the center of the contact lens. The first surface is formed in a concave shape having a curvature less than that of the central surface of the patient&#39;s cornea. The contact lens further includes a relief zone having a concave-shaped second surface defined by the inner surface of the contact lens located on the side of the patient&#39;s cornea and positioned at the periphery of the pressure zone, and an anchor zone having a concave-shaped third surface defined by the inner surface of the contact lens on the side of the patient&#39;s cornea and positioned at the periphery of the relief zone. The first surface has a curvature determined based on the shape of the patient&#39;s cornea to induce a specific desired alteration in the shape of the patient&#39;s cornea. Further, each of the curvatures of the first, second and third surfaces is arranged to satisfy the following formulas, 
       RC=BC+ 7.0˜9.0  D  ( diopter ),  and   
       AC=BC+ 2.0˜4.0 D   
     where BC is the curvature of the first surface, RC is the curvature of the second surface, and AC is the curvature of the third surface.

FIELD OF THE INVENTION

[0001] The present invention relates to a contact lens for correctingmyopia and/or astigmatism. More specifically, the present inventionrelates to a myopia and/or astigmatism-correcting contact lens forreshaping the cornea based upon corneal topography to effect correctionof visual defects.

BACKGROUND OF THE INVENTION

[0002] Visual or optical defects which prevent parallel light raysentering the eye from focusing clearly on the retina exist in severalvarieties. In hyperopia (farsightedness), the point of focus lies behindthe retina, generally because the axis of the eyeball is too short. Inmyopia (nearsightedness), the image is focused in front of the retina,generally because the axis of the eyeball is too long. In astigmatism,refraction is unequal on the different meridians of the eyeball,generally due to asymmetry in the shape of the eye.

[0003] Corrective glasses or contact lenses have been used to correctthese defects, including convex (plus) lenses for hyperopia, concave(minus) lenses in myopia, and cylindrical lenses in astigmatism. Morerecently, a surgical technique, myopic or hyperopic keratomileusis hasbeen used to alter cornea curvature and thereby improve refractiveerror. This method cuts and removes a predicted thickness of the cornealdisk with a microkeratome. Additional surgical procedures such as radialkeratotomy use microincisions in the cornea to surgically modify thecurvature of the cornea and thereby reduce or eliminate myopia orastigmatism.

[0004] Photorefractive keratectomy (PRK) uses a laser to ablate thecenter of the cornea and thus change the cornea. In Automated LamilarKeratectomy (ALK) pressure is placed on the cornea to bulge the centraldome. A flap in the dome is then opened, layers of corneal tissue areremoved and the flap is then closed. Procedures combining aspects ofALK/PRK are sometimes used, called LASIK (laser in situ keratectomy).

[0005] While these surgical procedures effect long lasting correction ofvisual defects, they present an inherent risk of permanent damage to apatient's eye. However slight this risk might be, many patients areunwilling to undergo these surgical procedures to correct the curvatureof the cornea. Thus, there has existed a need to provide a non-surgicalmethod for reshaping the cornea and thereby effecting correction ofvisual defects.

[0006] As one technique for satisfying such a demand, U.S. Pat. No.5,695,509 provides an optical contact lens (contact lens) fornon-surgically reshaping and altering the curvature of the cornea. Whenapplied to the cornea of a patient, this optical contact lens(hereinafter, sometime referred to as “contact lens”) exerts a selectivepressure on the cornea causing displacement of corneal tissue away froma pressure zone to a relief zone, thereby reshaping the patient's corneaand improving the patient's vision without surgical intervention. Ingeneral, the design of the optical contact lens induces change in thecorneal topography of the patient's eye to make the cornea of a myopiceye more oblate.

[0007] This optical contact lens is tooled in response to the specificcontour or topography of a patient's cornea and to affect a desiredreshaping or correction of the eye's curvatures. When the contact lensis placed on the patient's cornea, a pressure zone of the contact lensexerts a relative selective pressure on the underlying or engaged regionof the cornea to effect displacement of corneal tissue away from theregion of pressure. A relief zone adjacent to the pressure zone does notcontact the cornea and does not exert pressure on the cornea, but is anarea where the contact lens is raised above the corneal surface. Thisarea serves to receive corneal tissue which is displaced from the corneaunderlying the pressure zone. An anchor zone adjacent to the relief zoneand between the relief zone and the periphery of the contact lenscontrols or guides the reshaping of the corneal tissue, directingdisplaced tissue to the relief zone. The anchor zone also ensures goodcentration and maintenance of centration of the contact lens on thecornea thus providing predictability of the result and preventingovershooting the desired correction.

[0008] A contact lens of this invention useful in the treatment ofmyopia contains a central pressure zone, an adjacent annular reliefzone, and an annular anchor zone adjacent to the relief zone and locatedbetween the relief zone and the periphery of the contact lens. When thecontact lens is positioned on the patient's cornea, pressure is exertedby the central pressure zone on the approximate center of the cornealdome, thereby effecting displacement of corneal tissue away from thecenter of the dome and to the adjacent annular relief area. The pressureexerted at the anchor zone controls reformation of the corneal surfaceby guiding the displaced tissue into the relief zone. With time, thesteep curvature of the myopic eye's corneal dome is flattened orreduced, and light incident over the central cornea will more correctlyconverge on the retina, thereby improving the patient's vision.

[0009] In order to effect the treatment of astigmatism for a patient'scorneal dome having one or more curvatures, the contact lens' curvatureis arranged in each of given axes to allow the pressure zone to bepositioned so as to apply pressure at the steepest meridian, therebyreducing the steep meridian and minimizing or eliminating the differencein curvature. The characteristics of a contact lens for treatingastigmatism are similar to those of a contact lens for correctingmyopia.

[0010] The contact lens provided by the above U.S. Patent can besummarized as follows.

[0011] A myopia and/or astigmatism-correcting contact lens forcorrecting myopia and/or astigmatism based upon the alteration in theshape of a patient's cornea, comprising;

[0012] a pressure zone having a first surface defined by the innersurface of the contact lens located on the side of a patient's corneaand positioned at the center of the contact lens, wherein the firstsurface is formed in a concave shape having a curvature than that of thecentral surface of the patient's cornea;

[0013] a relief zone having a second surface defined by the innersurface of the contact lens located on the side of the patient's corneaand positioned at the periphery of the pressure zone, wherein the secondsurface is formed in a concave shape; and

[0014] an anchor zone having a third surface defined by the innersurface of the contact lens located on the side of the patient's corneaand positioned at the periphery of the relief zone and, wherein thethird surface is formed in a concave shape.

[0015] More specifically, in order to induce a specific desiredalteration in the shape of the patient's cornea, the first surface has acurvature determined based on the shape of the patient's cornea, andeach of the curvatures of the first, second and third surfaces isarranged to satisfy the following formulas,

RC=BC+3.00 D (diopter), and

AC=BC+0.0-1.0 D

[0016] where BC is the curvature of the first surface, RC is thecurvature of the second surface, and AC is the curvature of the thirdsurface.

[0017] The contact lens having the RC and AC arranged as above couldachieve some positive results. However, it was significantly effectiveonly for European and American but less effective for Asian. Thus, theinventors have researched the shape of the cornea of Asian, particularlyof Japanese, and have found out a desirable curvature of each of theaforementioned surfaces of the contact lens most effective for Asian,particularly for Japanese.

DISCLOSURE OF THE INVENTION

[0018] Based on this knowledge, it is an object of the present inventionto provide a myopia and/or astigmatism-correcting contact lens having acurvature effective for Asian, particularly for Japanese.

[0019] According to the first aspect of the present invention, a myopiaand/or astigmatism-correcting contact lens for correcting myopia and/orastigmatism based on the alteration in the shape of a patient's cornea,said myopia and/or astigmatism-correcting contact lens comprising;

[0020] a pressure zone having a first surface defined by the innersurface of said contact lens located on the side of the patient's corneaand positioned at the center of said contact lens, said first surfacebeing formed in a concave shape having a curvature less than that of thecentral surface of the patient's cornea;

[0021] a relief zone having a second surface defined by the innersurface of said contact lens located on the side of the patient's corneaand positioned at the periphery of said pressure zone, said secondsurface being formed in a concave shape; and

[0022] an anchor zone having a third surface defined by the innersurface of said contact lens on the side of the patient's cornea andpositioned at the periphery of said relief zone, said third surfacebeing formed in a concave shape, wherein

[0023] said first surface has a curvature determined based on the shapeof the patient's cornea to induce a specific desired alteration in theshape of the patient's cornea, and

[0024] each of the curvatures of said first, second and third surfacesis arranged to satisfy the following formulas,

RC=BC+7.0˜9.0 D (diopter), and

AC=BC+2.0˜4.0 D

[0025]  where BC is the curvature of the first surface, RC is thecurvature of the second surface, and AC is the curvature of the thirdsurface.

[0026] It is preferred that, in the above myopia and/orastigmatism-correcting contact lens, each of the curvatures of saidfirst, second and third surfaces is arranged to satisfy the followingformulas,

RC=BC+7.5˜8.5 D, and

AC=BC+2.5˜3.5 D

[0027] Alternatively, each of the curvatures of said first, second andthird surfaces is preferably arranged to satisfy the following formulas,

RC=BC+about 8.0 D, and

AC=BC+about 3.0 D

[0028] The myopia and/or astigmatism-correcting preferably has adiameter ranging from about 9.0 to about 11.0 mm, and more preferable,about 9.5 to about 10.5 mm, and especially preferable, about 10 mm.

[0029] According to the second aspect of the present invention, a myopiaand/or astigmatism-correcting contact lens for correcting myopia and/orastigmatism based on the alteration in the shape of a patient's cornea,said myopia and/or astigmatism-correcting contact lens comprising;

[0030] a pressure zone having a first surface defined by the innersurface of said contact lens located on the side of a patient's corneaand positioned at the center of said contact lens, said first surfacebeing formed in a concave shape having a curvature less than that of thecentral surface of the patient's cornea;

[0031] a relief zone having a second surface defined by the innersurface of said contact lens located on the side of the patient's corneaand positioned at the periphery of said pressure zone, said secondsurface being formed in a concave shape;

[0032] a first anchor zone having a third surface defined by the innersurface of said contact lens on the side of the patient's cornea andpositioned at the periphery of said relief zone, said third surfacebeing formed in a concave shape; and

[0033] a second anchor zone having a fourth surface defined by the innersurface of said contact lens on the side of the patient's cornea andpositioned at the periphery of said first anchor zone, said fourthsurface being formed in a concave shape, wherein

[0034] said first surface has a curvature determined based on the shapeof the patient's cornea to induce a specific desired alteration in theshape of the patient's cornea, and

[0035] each of the curvatures of said first, second, third and fourthsurfaces is arranged to satisfy the following formulas,

RC=BC+11.00-13.0 D

AC 1=BC+3.0-5.0 D, and

AC 2=BC+4.0-6.0 D

[0036] where BC is the curvature of the first surface, RC is thecurvature of the second surface, AC 1 is the curvature of the thirdsurface, and AC 2 is the curvature of the fourth surface.

[0037] It is preferred that, in the above myopia and/orastigmatism-correcting contact lens, each of the curvatures of saidfirst, second, third and fourth surfaces is arranged to satisfy thefollowing formulas,

RC=BC+11.5- 12.5 D,

AC 1=BC+3.5-4.5 D and

AC 2=BC+4.5-5.5 D

[0038] Alternatively, each of the curvatures of said first, second,third and fourth surfaces is preferably arranged to satisfy thefollowing formulas,

RC=BC+about 12 D,

AC 1=BC+about 4 D, and

AC 2=BC+about 5 D

[0039] According to the third aspect to the present invention, a myopiaand/or astigmatism-correcting contact lens for correcting myopia and/orastigmatism based on the alteration in the shape of a patient's cornea,said myopia and/or astigmatism-correcting contact lens comprising;

[0040] a pressure zone having a first surface defined by the innersurface of said contact lens located on the side of a patient's corneaand positioned at the center of said contact lens, said first surfacebeing formed in a concave shape having a curvature less than that of thecentral surface of the patient's cornea;

[0041] a relief zone having a second surface defined by the innersurface of said contact lens located on the side of the patient's corneaand positioned at the periphery of said pressure zone, said secondsurface being formed in a concave shape;

[0042] a first anchor zone having a third surface defined by the innersurface of said contact lens on the side of the patient's cornea andpositioned at the periphery of said relief zone, said third surfacebeing formed in a concave shape; and

[0043] a second anchor zone having a fourth surface defined by the innersurface of said contact lens on the side of the patient's cornea andpositioned at the periphery of said first anchor zone, said fourthsurface being formed in a concave shape, wherein

[0044] said first surface has a curvature determined based on the shapeof the patient's cornea to induce a specific desired alteration in theshape of the patient's cornea, and

[0045] each of the curvatures of said first, second, third and fourthsurfaces is arranged to satisfy the following formulas,

RC=BC+12.5-14.5 D,

AC 1=BC+3.0-5.0 D, and

AC 2=BC+4.0-6.0 D

[0046]  where BC is the curvature of the first surface, RC is thecurvature of the second surface, AC 1 is the curvature of the thirdsurface, and AC 2 is the curvature of the fourth surface.

[0047] It is preferred that in the above myopia and/orastigmatism-correcting contact lens as defined in claim 10, wherein eachof the curvatures of said first, second, third and fourth surfaces isarranged to satisfy the following formulas,

RC=BC+13.0-14.0 D,

AC 1=BC+3.5-4.5 D, and

AC 2=BC+4.5-5.5 D

[0048] Alternatively, each of the curvatures of said first, second,third and fourth surfaces is preferably arranged to satisfy thefollowing formulas,

RC=BC+about 13.5 D,

AC 1=BC+about 4 D, and

AC 2=BC+about 5 D

[0049] The myopia and/or astigmatism-correcting contact lens may have adiameter ranging from about 9.6 to about 11.6 mm, preferable about 10.1to about 11.6 mm, more preferable, about 10.6 to about 11.2 mm, andespecially preferable, about 10.2, 10.4, 10.6, 10.8, and 11.0 mm.

[0050] As with the optical contact lens of the aforementioned U.S.Patent, in a myopia and/or astigmatism-correcting contact lens of thepresent invention, application of this contact lens to a patient'scornea results in reshaping of the cornea and provides improved visualacuity. In a preferred embodiment, once a patient's cornea has achievedan optimal shape, as determined by functional visual acuity, the contactlens of the present invention may be temporarily removed without loss ofvisual correction. However, a patient may maintain the desired shape ofthe cornea by wearing the optical contact lens for a short period oftime, e.g., approximately three to eight hours per day. For example, insome instances, a patient may wear the contact lens one or two nights aweek or every night during sleep to maintain the desired shape andfunctional vision.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051]FIG. 1 is a schematic side sectional view of an average normaleye;

[0052]FIG. 2 is a schematic sectional view of a myopic eye;

[0053]FIG. 3 is a schematic sectional view of an astigmatic eye;

[0054]FIG. 4 is a schematic sectional view of a contact lens accordingto a first embodiment of the present invention suitable for treating themyopic eye of FIG. 2; and

[0055]FIG. 5 is a schematic sectional view of a contact lens accordingto second and third embodiments of the present invention suitable fortreating the myopic eye of FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0056] In order to help understanding of a myopia and/orastigmatism-correcting contact lens according to a preferred embodimentof the invention, the general state of eyes will be first described withreferred to FIGS. 1 to 3.

[0057]FIG. 1 shows a normal eye containing a normal cornea 2. Theportion of the cornea 2 which projects over the lens 5 is termed thecorneal dome 4. The corneal dome 4 is generally considered rotationallysymmetrical and aspherical in shape, with the approximate dome center 6having essentially the highest projection away from the center of theeye. A generally circular optical zone o transmits incident light whichnormally converges on the retina 7.

[0058] Defects in visual acuity are correlated with distortions in theshape of the cornea. As shown in FIG. 2, convergence occurs in front ofthe retina in a myopic eye (nearsighted), and is associated with anelongated axis a and a steepened or heightened corneal dome 4. In an eyehaving astigmatism, multiple curvatures of the cornea cause multipleareas of convergence as shown in FIG. 3.

[0059] The degree of corneal distortion and precise location and size ofa patient's corneal dome center 6 and dome periphery 8 may be determinedby one of skill in the art using a videokeratoscope or cornealtopographer. As described in pending U.S. application Ser. No.08/046,619, measurements of the contour of the cornea of the human eyehave been used to facilitate the design and fit of contact lenses, aswell as for use and performance of surgical procedures.

[0060] In a conventional videokeratoscope used to measure the cornea,concentric rings of light from a source of light within a housing aredirected onto a cornea and reflected by the cornea onto the film of acamera as an image of the rings. The deviation of the rings from theirknown concentricity is measured and this data is processedmathematically to determine the actual contour of the cornea, which isnot a perfect sphere and which differs from one individual to another.Conventional photokeroscopes are disclosed, for example, in U.S. Pat.Nos. 3,248,162 and 3,598,478. Videokeratoscopes or corneal topographersare disclosed for example, in U.S. Pat. Nos. 4,978,213, 5,227,818 andU.S. patent application Ser. No. 08/046,619. In general, a cornealtopographer includes a camera means, such as a charged coupled devicecamera system for sensing the images of rings of light reflected fromthe cornea. The camera apparatus sends standard video signals to acomputer, such as a conventional, commercially available imageprocessor, which digitize the video signals. The computer analyzes thedigital data and produces data useful in determining the contour of thecornea of the human eye. A corneal topographer apparatus whichautomatically centers and focuses the corneal image reflected from apatient's cornea onto a charge coupled device camera system is disclosedin U.S. patent application Ser. No. 08/046,619.

[0061] Any of the above-described methods, as well as others known tothose of skill in the art, may be used to determine the topography ofthe cornea of a patient to be fitted with a contact lens of the presentinvention. Whatever method is utilized, the data is analyzed todetermine the corneal condition, e.g., regular, irregular, orastigmatism by methods generally known in the art. The location andcurvature of the corneal dome 4 and center 6 is determined. Using thesemeasurements, as well as the degree of refractive error to be corrected,a contact lens or a lens of the present invention is machined to applyselective pressure to areas of the patient's cornea in order to effect adesired displacement and reshaping of the cornea. Reformation orreshaping of the patient's cornea results in improvement of thepatient's vision.

[0062] The contour and shape of the contact lens L1 according to a firstembodiment are shown in FIG. 4 in an exaggerated form. The contour ofthe contact lens L1 is designed to treat myopia or astigmatism. In FIG.4, the contact lens L1 is symmetrical with respect to the axis X.

[0063] The contact lens L1 includes at its center a pressure zone 10which will overlay or engage a region of the corneal surface wherealteration is desired. When the contact lens L1 is placed on the eye,the pressure zone 10 will apply a relative pressure to the underlying orengaged region of the cornea. It is understood that the contact lens L1is separated from the cornea by fluid, e.g., tears present between thelens and the surface of the cornea but the fluid follows the contour ofthe cornea.

[0064] The contact lens L1 also includes an annular relief zone 12positioned at the periphery of the pressure zone 10. The relief zone 12is an area adjacent to the pressure zone 10 that creates a space or voidbetween the surface of cornea and the contact lens. No pressure isapplied from the relief zone 12 onto the underlying region of thecornea. In contrast to the pressure zone 10, the area between the reliefzone 12 and the underlying corneal surface is sufficiently spacious toreceive corneal tissue displaced by pressure applied at the pressurezone 10. An annular anchor zone 14 is located adjacent to the peripheryof the relief zone 12. The anchor zone 14 is in contact with the corneaand exerts minimal pressure on the cornea for purposes of anchoring thecontact lens on the corneal surface to achieve and maintain goodcentration or positioning. By applying relative pressure adjacent to therelief zone 12, the anchor zone 14 guides the displaced corneal tissueinto the area under the relief zone 12.

[0065] The position of the pressure zone 10 on the cornea is importantto the contact lens's function of providing useful reshaping of thecornea. Referring to FIG. 4, in a contact lens designed to treat myopia,the pressure zone 10 is positioned to apply pressure at the approximatecenter of the corneal dome. The anchor zone 14 maintains the contactlens's position on the cornea and controls the direction of cornealtissue displacement into the relief zone.

[0066] Preferably, the contact lens L1 of the present invention includesa second annular relief zone 16 at the periphery 18 of the contact lens.The second relief zone 16 is raised away from the cornea 2, e.g., toapproximately 80-100 μm at the periphery 18 of the contact lens, toassist in the movement of fluid and nutrients under the contact lens,and also to permit easy removal of the contact lens from the eye.

[0067] The specific location and size of the pressure zone, relief zone,anchor zone, and second relief zone will differ with the specificcondition of the patient's eye and corneal topography, and with the typeof correction desired.

[0068] As shown in FIG. 4, when the contact lens is applied to an eye,the pressure zone 10 engages the underlying corneal tissue. The term“Engages” means that portion of the contact lens is separated from thecorneal tissue essentially only by tear fluid, and the “engagement”causes pressure to be exerted by the pressure zone 10 of the contactlens onto the underlying corneal tissue. The pressure applied at thepressure zone 10 causes the underlying cornea to be displaced away fromthe pressure zone.

[0069] The relief zone 12 is that portion of the contact lens which,when positioned on an eye, does not “engage” the underlying cornea, butin contrast, is recessed or raised away from the cornea, creating anannular space or zone between the contact lens and the corneal surfacefor receiving displaced corneal tissue.

[0070] When the contact lens is applied to an eye, the annular anchorzone 14 engages the underlying cornea. The anchor zone 14 exerts aminimal pressure on the corneal surface underlying the contact lens at alocation adjacent to the relief zone 12 and between the relief zone 12and the periphery 18. The pressure exerted by the anchor zone 14cooperates with the central pressure zone 10 and guides displacedcorneal tissue into the space underlying the contact lens at the reliefzone 12. Pressure exerted by the anchor zone 14 also stabilizes thecontact lens on the corneal surface and permits achievement andmaintenance of good centration of the contact lens on the cornea. Likethe relief zone 12, a second relief zone 16 does not engage theunderlying cornea. The second relief zone 16 facilitates easy access offluid and nutrients under the contact lens and also permits easy “liftoff” or removal of the contact lens from the corneal surface. Ingeneral, the periphery 18 of the contact lens has a sufficient curvatureto be raised away from the cornea for access of fluids, e.g.,approximately 80-100 μm, and preferably about 90-100 μm.

[0071] The design of a contact lens to correct astigmatism of the eye asshown in FIG. 3 is in general similar to the contact lens of FIG. 4 fortreating a myopic eye.

[0072] The concave surface of the contact lens of the present inventionis formed with a continuous aspheric curvature from center to periphery,that is with a gradual change of curvature into each specified zone. Thecontinuous curve is achieved by machining the contact lens in accordancewith a mathematical analysis of the best curve fit for the desireddistances between the surface of the cornea at each of the specifiedzones and the contact lens.

[0073] The contact lens of the present invention may be fabricated frommaterials and using methods known to be useful, for example, in themanufacture of conventional contact lenses. Such materials include thoseuseful in fabricating conventional gas (oxygen) permeable contactlenses, e.g., fluroperm (Paragon Optical Co.) or any oxygenated rigidplastic available and known to be useful in fabrication of conventionalcontact lenses. An especially preferred lens material is fluroperm 60 or90, because it has high DK value (oxygen transmissibility). In apreferred embodiment, the contact lenses will also have opticalproperties to correct refractive error during the reshaping of thecornea.

[0074] The contact lenses of the present invention are machined toprovide the appropriate reshaping of a particular patient's eye. Theeye's corneal topography is defined and mapped using conventionalcorneal topography equipment as described above. The refraction of theeye is measured by conventional techniques. A diagnosis of the conditionto be treated is made, e.g., myopia or astigmatism, and the amount ofrefractive error is determined. The patient's corneal topography isanalyzed to select the appropriate parameters for the patient's contactlens, including the position, size and location of the corneal dome, theshape factor (e.g., deviation from a perfect sphere), and curvatures ofthe contact lens to match the patient's topography.

[0075] Measurements of a patient's corneal topography are adjusted forthe desired correction and used to specify the dimensions of thecorrective contact lens. For the myopic eye shown in FIG. 2, theapproximate size of the optical zone o, or heightened area of thecorneal dome is measured as the radius (or diameter) from theapproximate center of the dome 6 to the approximate mid-periphery 8.Generally, for a contact lens having a total diameter of about 10 mm,the diameter of the optical zone will vary from about 4 to about 7.5 mm.An area within the patient's optical zone o is analyzed to determine theaverage diopter of the optical zone, which determines the base diopterof the corrective contact lens. As shown in FIG. 4, the relative sizeand position, e.g., annular diameters of the pressure zone 10 and thediopter and annular diameter of the relief zone 12 is determined in partby the correction needed and the degree of the desired therapy.

[0076] The desired diopter of the pressure zone 10 is calculated toapply a relative pressure to the underlying cornea according to thediopter of cornea to be corrected, and is generally calculated bysubtracting a given value from the diopter of the cornea to becorrected, in which the given value is preferable to be 1.5-4.5,particularly about 3.

[0077] The factors disclosed in the aforementioned U.S. patent may beused as factors in addition to those described above and bellow.

[0078] The rate of curvedness (curvature) RC of the curve of the annularrelief zone 12 (the second surface) is machined to satisfy the followingformula, $\begin{matrix}{{RC} = {{BC} + 7.0 - {9.0D}}} \\{= {{BC} + 7.5 - {8.5{D({preferably})}}}} \\{= {{BC} + {{about}\quad 8.0{D\left( {{more}\quad {preferably}} \right)}}}}\end{matrix}$

[0079] where BC is the curvature of the curved surface of theaforementioned pressure zone (the first surface).

[0080] The rate of curvedness (curvature) RC of the curve of the anchorzone 14 (the third surface) is machined to satisfy the followingformula, $\begin{matrix}{{RC} = {{BC} + 2.0 - {4.0D}}} \\{= {{BC} + 7.5 - {8.5{D({preferably})}}}} \\{= {{BC} + {{about}\quad 8.0{D\left( {{more}\quad {preferably}} \right)}}}}\end{matrix}$

[0081] where BC is the curvature of the curved surface of theaforementioned pressure zone (the first surface).

[0082] Then, the contact lens is machined to provide a continuouscurvature from the annular anchor zone 14 through the second relief zone16 to the raised periphery 18 of the contact lens. The periphery 18 ofthe contact lens is machined to be raised approximately 80-100 μm fromthe surface of the cornea to provide edge lift.

[0083] The general diameter of the contact lens of the first embodimentis arranged in the range of about 9.0 to about 11.0 mm (4.5 to 5.5 mm inradius), preferably about 9.5 to about 10.5 mm (4.75 to 5.25 mm inradius), and most preferably about 10 mm (about 5 mm in radius).

[0084] The diameter of the central pressure zone 10 is arranged in therange of about 4 to 7.5 mm (2 to 3.75 mm in radius), preferably 4.5 to7.0 mm (2.25 to 3.5 mm in radius), and most preferably 5.8 to 6.5 mm(2.9 to 3.25 mm in radius). The annular radius of the relief zone isarranged preferably in the range of 0.5 to 1.0 mm, particularly at about0.7 mm. The annular radius of the anchor zone is arranged preferably inthe range of about 0.6 to about 0.8 mm. The annular radius of the secondrelief zone is arranged preferably in the range of 0.3 to 0.6 mm.

[0085] The method of forming a contact lens for the treatment ofastigmatism is similar to that for forming a contact lens to treat amyopic eye. The general diameter and average curvature of the opticalzone is determined. Next, the curvature of the pressure and relief zonesare calculated, as well as the anchor zone and second relief zonecurvatures.

[0086] The specific curvature of each contact lens is determined fromthe topography of the eye and the desired level of visual correctionneeded. One general method for calculating the curvatures of a contactlens for treating a myopic eye is described below. It is understood thatseveral methods may be used to achieve a contact lens of the presentinvention. Thus, the following description is meant to be exemplary, anddoes not limit the invention.

[0087] First, the patient's corneal topography is measured. Examining acentral portion of the cornea, e.g., the optical zone at about 4-5 mm incentral diameter (about 2-2.5 mm in central radius), an average diopteris determined.

[0088] After determining the average diopter of the center portion ofthe cornea, a desired diopter is arranged based on the determinedaverage diopter to provide a diopter of the pressure zone 10 of thecontact lens L1.

[0089] Each curvature of the relief zone and anchor zone of the contactlens to treat myopia is determined using the aforementioned formula.

[0090] The other factors may be determined by those described in theaforementioned U.S. patent.

[0091] After the patient has worn a contact lens of the presentinvention for a period of time, the patient is examined to recordprogress in reaching an optimal shape or optimal level of correction.For example, the patient may be examined approximately weekly or monthlyby measuring corneal topography and comparing new measurements ofcorneal shape and visual acuity with prior records. An optimal shape ofthe cornea is that shape which permits good correction of the patient'svisual defect to obtain functional vision, e.g., that vision acceptableto the patient without contact lenses.

[0092] For a very myopic patient, a plurality of contact lenses havingdifferent correction diopters may be prepared to allow the contact lensto be changeably worn depending on the progress in correction.

[0093] Examples of such contact lenses will be described bellow.

[0094] A contact lens L2 according to a second embodiment comprises: apressure zone 110 having a first surface defined by the inner surface ofthe contact lens located on the side of a patient's cornea andpositioned at the center of the contact lens, wherein the first surfaceis formed in a concave shape having a curvature less than that of thecentral surface of the patient's cornea; a relief zone 112 having asecond surface defined by the inner surface of the contact lens locatedon the side of the patient's cornea and positioned at the periphery ofthe pressure zone 111, wherein the second surface is formed in a concaveshape; a first anchor zone 114 a having a third surface defined by theinner surface of the contact lens on the side of the patient's corneaand positioned at the periphery of the relief zone 112, wherein thethird surface is formed in a concave shape; and a second anchor zone 114b having a fourth surface defined by the inner surface of the contactlens on the side of the patient's cornea and positioned at the peripheryof the first anchor zone 114 a, wherein the fourth surface is formed ina concave shape.

[0095] The contact lens L2 has the curved surfaces arranged to satisfythe following formulas,

RC=BC+11.00-13.0 D

AC 1=BC+3.0-5.0 D, and

AC 2=BC+4.0-6.0 D

[0096] where BC is the curvature of the first surface, RC is thecurvature of the second surface, AC 1 is the curvature of the thirdsurface, and AC 2 is the curvature of the fourth surface.

[0097] Preferably, the above relationship is arranged as follows,

RC=BC+11.5-12.5 D,

AC 1=BC+3.5-4.5 D, and

AC 2=BC+4.5-5.5 D

[0098] and, most preferably, the above relationship is arranged asfollows.

RC=BC+about 12 D,

AC 1=BC+about 4 D,

AC 2=BC+about 5 D

[0099] A contact lens L3 according to a third embodiment comprises apressure zone, a relief zone, a first anchor zone and a second anchorzone as with the contact lens L2 of the second embodiment. However,these are different in the relationship between respective curvatures ofthe surfaces as follows.

[0100] The contact lens L3 has the curved surfaces arranged to satisfythe following formulas,

RC=BC+12.5-14.5 D

AC 1=BC+3.0-5.0 D, and

AC 2=BC+4.0-6.0 D

[0101] where BC is the curvature of the first surface, RC is thecurvature of the second surface, AC 1 is the curvature of the thirdsurface, and AC 2 is the curvature of the fourth surface.

[0102] Preferably, the above relationship is arranged as follows,

RC=BC+13.0-14.0 D,

AC 1=BC+3.5-4.5 D, and

AC 2=BC+4.5-5.5 D,

[0103] and, more preferably, the above relationship is arranged asfollows.

RC=BC+about 13.5 D,

AC 1=BC+about 4 D, and

AC 2=BC+about 5 D

[0104] The diameters of the contact lens L2 and L3 are approximately thesame and arranged preferably in the range of about 9.6 to about 11.6 mm,more preferably about 10.1 to about 11.3 mm, further 10.6 to 11.2 mm,and are specifically arranged at either one of about 10.2, 10.4, 10.6,10.8, and 11.0 mm.

[0105] The diameter of the central pressure zone 110 is arranged in therange of about 4 to about 7.5 mm (2 to 3.75 mm in radius), preferably4.5 to 7.0 mm (2.25 to 3.5 mm in radius), more preferably 5.8 to 6.5 mm(2.9 to 3.25 mm in radius). The annular radius of the relief zone 112 isarranged preferably in the range of 0.5 to 1.0 mm, particularly at about0.7 mm. The annular radius of the first anchor zone 114 a is arrangedpreferably in the range of about 0.5 to about 0.9 mm, particularly atabout 0.6 mm. The annular radius of the second anchor zone 114 b isarranged preferably in the range of about 0.4 to about 0.9 mm,particularly at about 0.6 mm. The second relief zone 116 is provided atthe outer periphery of the second anchor zone 114 b, and an annularradius of the second anchor zone 114 b is arranged preferably in therange of about 0.3 to about 0.6 mm, particularly at about 0.4 mm.

[0106] The following examples will be referred to help betterunderstanding of the invention.

EXAMPLES Example 1 (with the Features of the Contact Lens L1 of theFirst Embodiment)

[0107] A Japanese patient A initially wore a soft contact lens every dayto correct myopia. The patient was diagnosed with myopia through themeasurement of refractive error. According to the measurement of thetopography of central curves of the right and left eyes, the diopter ofthe right eye was 38.50 (refractive error: −4.25, uncorrected vision:0.1) and the diopter of the left eye was 39.00 (refractive error: −4.00,uncorrected vision: 0.1).

[0108] Based on the above measurements, BCs of the contact lenses of thepatient's right and left eyes were arranged at 35.50 D and 36.00 D,respectively.

[0109] Then, according to the present invention, RC and AC weredetermined using the following two formulas.

RC=BC+8.0 D

AC=BC+3.0 D

[0110] As a result, RC and AC of the right eye's contact lens were 43.50D and 38.50 D, respectively. Further, RC and AC of the left eye'scontact lens were 44.0 D and 39.00 D, respectively.

[0111] Then, the general diameter of the contact lens was arranged at 10mm, the diameter of the central pressure zone 10 being arranged at 6.0mm (3.00 mm in radius), the annular radius of the relief zone 12 beingarranged at 0.7 mm, the annular radius of the anchor zone 14 beingarranged at 0.7 mm, and the annular radius of the second relief zonebeing arranged at 0.6 mm.

[0112] By using the above parameters, the contact lens L1 having theconfiguration of the example 1 shown in FIG. 4 was fabricated.

[0113] On the other hand, RC and AC were determined using the followingtwo formulas which have heretofore been used in U.S. as described above.

RC=BC+3.0 D

AC=BC+0.0 D

[0114] As a result, RC and AC of the right eye's contact lens were 38.50D and 35.50 D, respectively. RC and AC of the left eye's contact lenswere 39.00 D and 36.00 D, respectively.

[0115] Then, using the same diameters as those of the inventive example,a contact lens as a comparative example was fabricated.

[0116] The contact lenses of the inventive example and the comparativeexample were worn by the patient A, and their results were compared witheach other.

[0117] More specifically, the contact lenses as the comparative examplewere first worn by the myopic patient A at bedtime of night for oneweek. As a result, the right and left eyes of the patient A had 37.75diopter (refractive error: −3.50, uncorrected vision: 0.2) and 38.00diopter (refractive error: −3.25, uncorrected vision: 0.3),respectively, and some improvement was observed. However, once quittingthe wearing, the original state was brought back in a week.

[0118] After that, the contact lenses according to the example 1 of theinvention were worn by the patient A in the same way as that of thecomparative example. As a result, the right and left eyes of the patientA had 37.00 diopter (refractive error: −1.75, uncorrected vision: 0.9)and 37.00 diopter (refractive error: −1.50, uncorrected vision: 1.0),respectively, and significant improvement was observed. Then, after thepatient A continued the wearing under the above condition for a month,the effect was measured. As a result, the right and left eyes of thepatient A had 36.25 diopter (refractive error: −0.25, uncorrectedvision: 1.5) and 36.00 diopter (refractive error: −0.25, uncorrectedvision: 1.5), respectively. Thus, the effect has been apparently proved.

Examples 2 and 3 (with the Features of the Contact Lenses L2 and L3 ofthe Second and Third Embodiments)

[0119] A Japanese patient B initially wore a soft contact lens every dayto correct myopia. The patient was diagnosed with myopia through themeasurement of refractive error. According to the measurement of thetopography of central curves of the right and left eyes, the diopter ofthe right eye was 41.25 (refractive error: −6.25, uncorrected vision:0.01) and the diopter of the left eye was 41.50 (refractive error:−6.50, uncorrected vision: 0.01 ).

[0120] Based on the above measurements, BCs of the contact lenses of thepatient's right and left eyes were arranged at 38.25 D and 38.50 D,respectively.

[0121] Then, according to the present invention, RC, AC 1 and AC 2 weredetermined using the following three formulas.

RC=BC+12.0 D

AC 1=BC+5.0 D

AC 2=BC+4.0 D

[0122] As a result, RC, AC 1 and AC 2 of the right eye's contact lens ofthe example 2 were 50.25 D, 43.25 D and 42.25 D, respectively. Further,RC, AC 1 and AC 2 of the left eye's contact lens were 50.50 D, 43.50 Dand 42.50 D, respectively.

[0123] Then, for the contact lens of the example 3, RC, AC 1 and AC 2were determined using the following three formulas.

RC=BC+13.5 D

AC 1=BC+5.0 D

AC 2=BC+4.0 D

[0124] As a result, RC, AC 1 and AC 2 of the right eye's contact lens ofthe example 3 were 51.75 D, 43.25 D and 42.25 D, respectively. Further,RC, AC 1 and AC 2 of the left eye's contact lens were 52.00 D, 43.50 Dand 42.50 D, respectively.

[0125] Then, the general diameter of the contact lenses according to theexample 2 and 3 was arranged at 10 mm, the diameter of the centralpressure zone 10 being arranged at 6.0 mm (3.00 mm in radius), theannular radius of the relief zone 12 being arranged at 0.7 mm, theannular radius of the first anchor zone 14 being arranged at 0.6 mm, theannular radius of the second anchor zone being arranged at 0.6 mm, andthe annular radius of the second relief zone being arranged at 0.4 mm.

[0126] By using the above parameters, the contact lenses L2 and L3having the configurations of the examples 2 and 3 shown in FIG. 5 werefabricated.

[0127] On the other hand, RC and AC were determined using the followingtwo formulas which have heretofore been used in U.S. as described above.

RC=BC+3.0 D

AC=BC+0.0 D

[0128] As a result, RC and AC of the right eye's contact lens were 41.25D and 38.25 D, respectively. RC and AC of the left eye's contact lenswere 41.50 D and 38.50 D, respectively.

[0129] Then, using the same diameters as those of the example 1, acontact lens as a comparative example 2 was fabricated.

[0130] The contact lenses of the examples 2 and 3 and the comparativeexample 2 were worn by the patient B, and their results were comparedwith each other.

[0131] More specifically, the contact lenses of the comparative example2 were worn by the patient B at bedtime of night for one week. As aresult, the right and left eyes of the patient B had 40.75 diopter(refractive error: −5.50, uncorrected vision: 0.08) and 40.50 diopter(refractive error: −5.75, uncorrected vision: 0.07), respectively, andsome improvement was observed. However, once quitting the wearing, theoriginal state was brought back in a week.

[0132] After that, the contact lenses according to the example 2 of theinvention were worn by the patient B in the same way as that of thecomparative example. As a result, the right and left eyes of the patientB had 39.75 diopter (refractive error: −4.25, uncorrected vision: 0.2)and 39.50 diopter (refractive error: −4.00, uncorrected vision: 0.3),respectively, and significant improvement was observed. Then, after thepatient B continued the wearing under the above condition for a month,the effect was measured. As a result, the right and left eyes of thepatient B had 39.25 diopter (refractive error: −2.50, uncorrectedvision: 0.7) and 39.00 diopter (refractive error: −2.25, uncorrectedvision: 0.8), respectively.

[0133] After that, the contact lenses according to the example 3 of theinvention were successively worn by the patient B in the same way asthat of the example 2. As a result, the right and left eyes of thepatient B had 38.25 diopter (refractive error: −0.50, uncorrectedvision: 1.5) and 38.50 diopter (refractive error: −0.75, uncorrectedvision: 1.2), respectively, and more significant improvement wasobserved.

[0134] As above, the effect of the present invention has been apparentlyproved. Further, when the contact lenses prepared by the techniqueaccording to the present invention were worn by an astigmatic patient, asimilar same effect to that in the case of myopia could be obtained

[0135] The above results demonstrate the effect of the presentinvention.

What is claimed is:
 1. A myopia and/or astigmatism-correcting contactlens for correcting myopia and/or astigmatism based on the alteration inthe shape of a patient's cornea, said myopia and/orastigmatism-correcting contact lens comprising; a pressure zone having afirst surface defined by the inner surface of said contact lens locatedon the side of the patient's cornea and positioned at the center of saidcontact lens, said first surface being formed in a concave shape havinga curvature less than that of the central surface of the patient'scornea; a relief zone having a second surface defined by the innersurface of said contact lens located on the side of the patient's corneaand positioned at the periphery of said pressure zone, said secondsurface being formed in a concave shape; and an anchor zone having athird surface defined by the inner surface of said contact lens on theside of the patient's cornea and positioned at the periphery of saidrelief zone, said third surface being formed in a concave shape,whereinsaid first surface has a curvature determined based on the shape of thepatient's cornea to induce a specific desired alteration in the shape ofthe patient's cornea, and each of the curvatures of said first, secondand third surfaces is arranged to satisfy the following formulas,RC=BC+7.0˜9.0 D (diopter), and AC=BC+2.0˜4.0 D where BC is the curvatureof the first surface, RC is the curvature of the second surface, and ACis the curvature of the third surface.
 2. A myopia and/orastigmatism-correcting contact lens as defined in claim 1, wherein eachof the curvatures of said first, second and third surfaces is arrangedto satisfy the following formulas, RC=BC+7.5˜8.5 D, and AC=BC+2.5˜3.5 D3. A myopia and/or astigmatism-correcting contact lens as defined inclaim 1, wherein each of the curvatures of said first, second and thirdsurfaces is arranged to satisfy the following formulas, RC=BC+about 8.0D, and AC=BC+about 3.0 D
 4. A myopia and/or astigmatism-correctingcontact lens as defined in either one of claim 1, which has a diameterranging from about 9.0 to about 11.0 mm.
 5. A myopia and/orastigmatism-correcting contact lens as defined in either one of claim 1,which has a diameter ranging from about 9.5 to about 10.5 mm.
 6. Amyopia and/or astigmatism-correcting contact lens as defined in eitherone of claim 1, which has a diameter of about 10 mm.
 7. A myopia and/orastigmatism-correcting contact lens for correcting myopia and/orastigmatism based on the alteration in the shape of a patient's cornea,said myopia and/or astigmatism-correcting contact lens comprising; apressure zone having a first surface defined by the inner surface ofsaid contact lens located on the side of a patient's cornea andpositioned at the center of said contact lens, said first surface beingformed in a concave shape having a curvature less than that of thecentral surface of the patient's cornea; a relief zone having a secondsurface defined by the inner surface of said contact lens located on theside of the patient's cornea and positioned at the periphery of saidpressure zone, said second surface being formed in a concave shape; afirst anchor zone having a third surface defined by the inner surface ofsaid contact lens on the side of the patient's cornea and positioned atthe periphery of said relief zone, said third surface being formed in aconcave shape; and a second anchor zone having a fourth surface definedby the inner surface of said contact lens on the side of the patient'scornea and positioned at the periphery of said first anchor zone, saidfourth surface being formed in a concave shape, wherein said firstsurface has a curvature determined based on the shape of the patient'scornea to induce a specific desired alteration in the shape of thepatient's cornea, and each of the curvatures of said first, second,third and fourth surfaces is arranged to satisfy the following formulas,RC=BC+11.00-13.0 D AC 1=BC+3.0-5.0 D, and AC 2=BC+4.0-6.0 D  where BC isthe curvature of the first surface, RC is the curvature of the secondsurface, AC 1 is the curvature of the third surface, and AC 2 is thecurvature of the fourth surface.
 8. A myopia and/orastigmatism-correcting contact lens as defined in claim 7, wherein eachof the curvatures of said first, second, third and fourth surfaces isarranged to satisfy the following formulas, RC=BC+11.5-12.5 D, AC1=BC+3.5-4.5 D and AC 2=BC+4.5-5.5 D
 9. A myopia and/orastigmatism-correcting contact lens as defined in claim 7, wherein eachof the curvatures of said first, second, third and fourth surfaces isarranged to satisfy the following formulas, RC=BC+about 12 D, AC1=BC+about 4 D, and AC 2=BC+about 5 D
 10. A myopia and/orastigmatism-correcting contact lens as defined in claim 7, which has adiameter ranging from about 9.6 to about 11.6 mm.
 11. A myopia and/orastigmatism-correcting contact lens as defined in claim 7, which has adiameter ranging from about 10.1 to about 11.6 mm.
 12. A myopia and/orastigmatism-correcting contact lens as defined in claim 7, which has adiameter ranging from about 10.6 to about 11.2 mm.
 13. A myopia and/orastigmatism-correcting contact lens as defined in claim 7, which has adiameter of either one of about 10.2, 10.4, 10.6, 10.8, and 11.0 mm. 14.A myopia and/or astigmatism-correcting contact lens for correctingmyopia and/or astigmatism based on the alteration in the shape of apatient's cornea, said myopia and/or astigmatism-correcting contact lenscomprising; a pressure zone having a first surface defined by the innersurface of said contact lens located on the side of a patient's corneaand positioned at the center of said contact lens, said first surfacebeing formed in a concave shape having a curvature less than that of thecentral surface of the patient's cornea; a relief zone having a secondsurface defined by the inner surface of said contact lens located on theside of the patient's cornea and positioned at the periphery of saidpressure zone, said second surface being formed in a concave shape; afirst anchor zone having a third surface defined by the inner surface ofsaid contact lens on the side of the patient's cornea and positioned atthe periphery of said relief zone, said third surface being formed in aconcave shape; and a second anchor zone having a fourth surface definedby the inner surface of said contact lens on the side of the patient'scornea and positioned at the periphery of said first anchor zone, saidfourth surface being formed in a concave shape, wherein said firstsurface has a curvature determined based on the shape of the patient'scornea to induce a specific desired alteration in the shape of thepatient's cornea, and each of the curvatures of said first, second,third and fourth surfaces is arranged to satisfy the following formulas,RC=BC+12.5-14.5 D, AC 1=BC+3.0-5.0 D, and AC 2=BC+4.0-6.0 D  where BC isthe curvature of the first surface, RC is the curvature of the secondsurface, AC 1 is the curvature of the third surface, and AC 2 is thecurvature of the fourth surface.
 15. A myopia and/orastigmatism-correcting contact lens as defined in claim 14, wherein eachof the curvatures of said first, second, third and fourth surfaces isarranged to satisfy the following formulas, RC=BC+13.0-14.0 D, AC1=BC+3.5-4.5 D, and AC 2=BC+4.5-5.5 D
 16. A myopia and/orastigmatism-correcting contact lens as defined in claim 14, wherein eachof the curvatures of said first, second, third and fourth surfaces isarranged to satisfy the following formulas, RC=BC+about 13.5 D, AC1=BC+about 4 D, and AC 2=BC+about 5 D
 17. A myopia and/orastigmatism-correcting contact lens as defined in claim 14, which has adiameter ranging from about 9.6 to about 11.6 mm.
 18. A myopia and/orastigmatism-correcting contact lens as defined in claim 14, which has adiameter ranging from about 10.1 to about 11.6 mm.
 19. A myopia and/orastigmatism-correcting contact lens as defined in claim 14, which has adiameter ranging from about 10.6 to about 11.2 mm.
 20. A myopia and/orastigmatism-correcting contact lens as defined in claim 14, which has adiameter of either one of about 10.2, 10.4, 10.6, 10.8, and 11.0 mm.